On Aug 30, 2014, at 7:38 PM, David Winsemius wrote:
On Aug 29, 2014, at 8:54 PM, David McPearson wrote:
On Fri, 29 Aug 2014 06:33:01 -0700 Jeff Newmiller <jdnew...@dcn.davis.ca.us
>
wrote
One clue is the help file for "$"...
?" $"
In particular there see the discussion of character indices and
the "exact"
argument.
<...snip...>
On August 29, 2014 1:53:47 AM PDT, Angel Rodriguez
<angel.rodrig...@matiainstituto.net> wrote: >
Dear subscribers,
I've found that if there is a variable in the dataframe with a name
<...sip...>
N <- structure(list(V1 = c(67, 62, 74, 61, 60, 55, 60, 59, 58),
V2 =
c(NA, 1, 1, 1, 1,1,1,1,NA)),
+ .Names = c("age","samplem"), row.names =
c(NA,
-9L), class = "data.frame")
N$sample[N$age >= 65] <- 1
N
age samplem sample
1 67 NA 1
2 62 1 1
3 74 1 1
4 61 1 1
5 60 1 1
6 55 1 1
7 60 1 1
8 59 1 1
9 58 NA NA
<...snip...>
Having seen all the responses about partial matching I almost
understand. I've
also replicated the behaviour on R 2.11.1 so it's been around
awhile. This
tells me it ain't a bug - so if any of the cognoscenti have the
time and
inclination can someone give me a brief (and hopefully simple)
explanation of
what is going on under the hood?
It looks (to me) like N$sample[N$age >= 65] <- 1 copies N$samplem
to N$sample
and then does the assignment. If partial matching is the problem
(which it
clearly is) my expectation is that the output should look like
age samplem
1 67 1
2 62 1
3 74 1
4 61 1
5 60 1
6 55 1
7 60 1
8 59 1
9 58 NA
That is - no new column.
(and I just hate it when the world doesn't live up to my
expectations!)
Not sure what you are seeing. I am seeing what you expected:
> test <- data.frame(age=1:10, sample=1)
> test$sample[test$age<5] <- 2
> test
age sample
1 1 2
2 2 2
3 3 2
4 4 2
5 5 1
6 6 1
7 7 1
8 8 1
9 9 1
10 10 1
I realized later that I had not constructed a test of you behavior and
that when I did I see the creation of a third column. The answer is to
read the help page:
?`[<-`
"Character indices can in some circumstances be partially matched (see
pmatch) to the names or dimnames of the object being subsetted (but
never for subassignment). "
Note the caveat in parentheses.
--
David Winsemius, MD
Alameda, CA, USA
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